Latch-trip circuit breakers



2 Sheets-Sheet 1 July 9, 1963 H. s. WINGARD x-:TAL

LATCH-TRIP Gramm BREAKERS Filed Nov. 1o, 1959 ATTORNEY HENRY s. MNTRS BY ful 2 Sheets-Sheet 2 INVENTORS H. S. WINGARD ETAL.

LATCH-TRIP CIRCUIT BREAKERS July 9, 1963 Filed Nov. 10, 1959 ATTORNEY United States Patent O 3,097,277 LATCH-TRIP CIRCUIT BREAKERS Henry S. Wingard, Cranford, and Alfred E. Maier, Colonia, N J., assignors to Federal Pacific Electric Conipany, a corporation of Delaware Filed Nov. 10, 1959, Ser. No. 852,013 17 Ciaims. (Cl. 20D-8.8)

This invention relates to circuit breakers and, more particularly, to molded-case multipole circuit breakers, with self-contained overcurrent release means.

One object of the present invention is in the provision of a circuit breaker, more particularly a circuit breaker of the enclosed molded-case type, having a substantially higher current rating than previous circuit breakers of corresponding proportions. A feature of the present invention resides in the provision of `a novel thermal control overload tripping mechanism which efficiently utilizes the heat developed by the conductors forming the current path through the circuit breaker for activating the bimetal. In this way the normal temperature rise within the circuit breaker is held -to a relatively low value. A circuit breaker of given proportions utilizing this novel feature can be rated at more than double the maximum cur-rent rating of previous commercial breakers of the same proportions.

In the novel circuit breaker disclosed in detail below, the current-responsive thermal overload release means is effectively related to an ambient temperature compensating device to realize the requisite current-response sensitivity despite the minimized current-induced temperature rise above ambient. Ambient temperature compensating bimetals have been used with indirectly heated currentresponsive bimetals in circuit breakers heretofore, mainly as a refinement. The current-induced temperature rise for activating the bimetals in known circuit breakers has been made `deliberately high in relation to the ambient temperature variation. A typical ambient temperature variation is C. whereas bimetal heating for over-current tripping has commonly required a temperature rise of 80-1l0 C. In one aspect of the present invention the inherent heating due to the overload current through the conduct-ors in the circuit breaker produces a much lower tempenature rise, typically 35 4G C. so that the ambient temperature variation becomes a larger, controlling factor, and yet the novel thermal tripping mechanism is efficiently utilized to produce reliable tripping performance when exposed to the practical range of ambient temperature variations. This yields the result of sharply increasing the current rating that is possible in a circuit breaker of given proportions. It is particularly significant in molded-case circuit breakers where the current-responsive bimetal and the ambient temperature bimetal lare both enclosed in the same space and where, therefore, the ambient temperature compensating bimetal is inevitably exposed in some degree to the heating due to the current through the breaker.

The current-responsive thermal control device is in intimate heat transfer relation with the conductors forming an essentially straight current path through the circuit breaker and thus utilizes the heating that is normally developed by such conductors. The previously used high-temperature resistance-element bimetal heaters are eliminated, eliminating the built-in heat source that caused a high temperature rise within the enclosure.

Another object and feature of the present invention resides in the provision of an improved mounting for the current-responsive bimetal. In the novel circuit breaker described hereinbelow, the enclosed current-responsive bimetal is carried by the same unitary bar that extends outside the enclosure to a terminal. This minimizes the number of internal heat-producing connections and simplifies 3,097,277 Patented July 9, 1963 the construction. Such bar Iis of heavy cross-.section and is secured in position in a manner to resist the stresses imposed by an external heavy conductor that is to be secured in the external terminal. The bimetal remains in stable heat-transfer relation to the bar and to the mechanism controlled by the bimetal.

Another object and feature of the present invention is the provision of an overload release which requires a much smaller operating force to trip the circuit breaker in response to an overload. The novel overload release includes a virtually frictionless latching mechanism for the contact operating mechanism whereby to effectively restrain the relatively heavy spring pressure in the contactoperating mechanism while at the same time providing for virtually frictionless overcurrent :release by thermal and magnetic current-responsive mechanism.

In the illustnative embodiment of the invention described in detail below spring levers are utilized to drive =a trip bar to release the cradle that forms part of the contact ope-rating mechanism, these spring levers being controlled by magnetic and thermal release mechanism. Pursuant to a further feature of the present invention such spring levers can be considerably softer than was heretofore feasible when used with the aforenoted frictionless latching mechanism. The advantages achieved by this arrangement include the considerable reduction of the frictional force lat the latch point of the spring lever so that a smaller operating force of the thermal control dev-ice will reliably effect tripping of the circuit breaker in response to an overload, under conditions of minimized temperature-rise. The magnetic tripping sensitivity is similarly enhanced. An additional important benefit is that the effort required to relatch the entire mechanism is considerably reduced because of the softer springs of said spring levers to be loaded in the relatching operation.

Another object and feature of the present invention lis the provision of a novel land improved magnetic overload release which functions for severe short-circuits for instantaneous release of t-he circuit breaker. A feature of the magnetic release mechanism is in lits adjustability over a wide range. In a practical example it can be adjusted to respond to any value of current from 25() amperes to 2500 amperes. In the novel circuit breaker a pivoted armature of the magnetic overload release is biased away from its companion pole piece by a biasing force which acts along a line close to the line between the pivot of the armature and the biasing connection thenewith and thus only slightly increased tension is developed during armature operation. Once movement of the armature is initiated in response to an overload, it tends to operate with a fast snap action. Oooperatively arranged with respect to the armature is a common member which is adjustable to both increase the magnetic air gap and the component of force exerted by the biasing means urging the armature away from the pole piece, this arrangement attaining the wide range of magnetic overload release adjustment mentioned previously.

A further feature of the present invention resides in the provision of an especially effective ambient temperature compensation arrangement, which takes on added significance in view of the relatively low tripping temperatures for operation of the current responsive bimetal. The ambient temperature compensation bimetal is disposed to be remote from the heating produced by the conductors forming the multipole current paths through the breaker, as compared to the current responsive bimetals which are in intimate heat trans-fer relation with such conductors. In the novel circuit Ibreaker the `ambient temperature compensation 'bimetal takes the form of a pivote-d latch for the contact operating mechanism responsive to both the thermal and magnetic current- ICC responsive mechanism, i.e., responsive to 'both the armature of the magnetic overload release and to the current responsive bimetal. This pivoted latch arrangement also aids inreducing the energy required to relatch the cradle subsequent to tripping. This ambient temperature compensating bimetal as a latching member is essentially in tension, and thus can be relatively thin and sensitive.

Yet another object of the present invention is the provision of Ia generally improved compact breaker of high rating which is of unique design and construction and which is `eminently lsuitable for its intended purposes.

The above and other objects, lfeatures and advantages of the present -invention will be more fully understood from the `following description of an illustrative embodiment of the invention considered in connection with the accompanying drawings forming part of the disclosure.

In the drawings:

FIG. 1 is a side elevational view, `shown partly in section to reveal the internal parts, of a circuit breaker embodying the present invention, the breaker being shown in a circuit open condition and the contact operating mechanism shown latched by the overload release mechanism;

FIG. 2 is a plan view thereof with parts broken iaway to reveal the internal parts;

FIG. 3 is a fragmentary plan view of a modified form of conductor; and

FIG. 4 is an `enlarged fragmentary side view showing a detail of the latch.

Referring now to the drawings, -a 'so-called moldedcase circuit breaker is illustrated having a cover 18 `and a base 12 of molded insulation conventionally secured to each `other so as to enclose `the contacts, the operating mechanism and the automatic over-load release mechanism. Terminals 14 and 16 are external connectors provided for connection to circuit wiring. Between these connectors there is a substantially straight-line current path through the circuit breakers, extending from terminal 14, along conductor 18, fixed contact 2l), moving contact 22, iiexible conductive braid 24, Iand conductor 26, to terminal 16. Conductor 26 is a substantially uniform bar of copper of rectangular cross-section. It has slight upward yoffset Aadjacent to terminal 16, so that both terminals 14 and 16 are `spaced equally from the bottom of the circuit breaker. A pair of mounting screws 28 unite conductor 26 mechanically to the molded base 12, thereby restraining iany force that might `be imposed by heavy external circuit conductors clamped in connector 16, to avoid displacement of conductor 26.

Conductive braid 24 has `a flat terminal piece 24 welded to it, and this is of relatively thin and ductile copper. Screw 30 extends through holes in conductors 26 and 24 to establish tight contact between these elements over a very broad area. Both elements 24 and 26 are silver-plated for minimizing contact resistance at this point. Screw 30 also grips the fixed end of current responsive bimetal 32 against conductor Z6, a lock washer 34 lbeing interposed to maintain contact pressure. The whole length of `bimetal 32 extends very close to conductor 26, and actually engages conductor 26 at normal temperatures and when no current is carried by conductor 26 lbinretal 32 has its high-expansion side 'facing conductor 26 so that it deflects upward in response to heating. Bimetal 32 forms part of the overload release mechanism to be described in `detail below.

As seen in FIG. 2 there are three side-by-side poles in the circuit breaker, and in each pole there is a current path including the elements 14, 18, 20, 22, 24, 26 and 16. Additionally a conventional overcenter lspring-andtoggle mechanism is provided in the center pole for mechanically operating the respective moving contacts 22 of the three poles. Each moving contact 22 is resiliently carried 'by contact carrier 36; and contact carriers 36 in turn rare united to a square insulating shaft 38 that extends all the way across the circuit breaker,`

shaft extensions 40 of square shaft 38 being suitably supported for rotation.

A pair of toggle links 42 and 44 are pivoted to each other at their knee 46. Lower link 42 is pivoted to the centerapole contact carrier 36 and upper toggle link 44 is pivoted to a releasable cradle 48 that is normally restrained by latching mechanism 50. Cradle 48 has a pivot 54 in stationary frame 52. A two-legged manual actuating lever 56 is pivotally supported at its lowerI extremity. Four springs 58 (only two being shown) are tensioned between knee 46 of the toggle at the lower ends of the springs and the :actuating lever 56 at Vthe upper ends of the springs. A lever extension or handle 60 of insulation is secured to actuating lever 56, and projects through a slot in the cover 18 so as to be accessible externally, this hlandle having usual lateral extensions t-hat close off the 'slot in all positions of the handle.

The ove-reenter spring-and-toggle mechanism illustrated is in its open condition; and by |operating handle 60 to the left in FIG. l, the springs are shifted so `as to cause the toggle to straighten and overcenter slightly, thereby to close the contacts of all three poles. In the closed condition of the circuit breaker, in the event that the latching `mechanism 5t) should release cradle 48, the cradle swings counterclockwise past the line of action `of these springs, resulting in collapse of the toggle and automatic opening ofthe contacts.

T-he foregoing contact operating mechanism is entirely conventional, forming part of the illustrative circuit breaker.

Latching mechanism 50 is contained in the same molded-case enclosure as the current paths of the respective poles. The individual current-responsive mechanisms of the several poles are coordinated by a co-mmon trip bar 62 that is journaled at its ends in the molded base 12. The latched surface of cradle 48 presses upward against roller 64; and the reduced-diameter end portions of roller 64 press upwardly against a pair of metal plates 66 that are riveted to upward internal extensions of trip bar 62 (FIG. 2). These reduced end portions of the latch roller can operate between horizontal limits dened by the walls of opposed pockets '68 formed in extensions 70. The legs of a generally U-shaped spring 72, secured to trip bar 62, biases roller 64 to the right. It will be apparent that, when trip bar 62 is rocked clockwise, it will cause roller 64 to roll with virtually no friction between the bearing surfaces of cradle 48 and metal plates 66 in the direction to release cradle 48 for automatic opening of the contacts. Spring 72 is relatively weak and is for the purpose of properly locating roller 64 during the resetting ope-ration following an overload release of the circuit breaker.

Resetting is accomplished by operating handle 60 from its on or its trip position towards the right so as to engage projection 48 of the cradle, driving the cradle clockwise against a reset arm 62 of the trip bar. Resulting counterclockwise rotation of the trip bar resets the individual current responsive mechanisms of the three poles.

An individual current responsive mechanism is provided in each pole, having both magnetic and thermal current responsive devices. Each such mechanism includes a stationary frame 74 secured to the molded base `12. Frame 74 pivotally supports a spring lever v76 that is biased -counterclockwise by a compression spring 78 on frame portion 80. Spring lever 76 is latched by an adjustable screw 82 on a pivoted latch member, formed as a temperature compensating bimetal 84. Latching engagement between screw 82 and spring lever 76 involves a force acting along a line passing through the pivot 86 substantially `at right angles to the line between the latching point and the pivot 88 of the latched spring lever 76. There is virtually no tendency of the spring biased lever 76 to operate the pivoted latch 82-84 in the releasing direction; and because screw 82 is only a negligible fraction of the length of member 84, there is almost pure tension developed in member 84. Consequently member 84 (a bimetal) can -be relatively thi-n and, therefore, sensitive. Compression spring 90 which bears against an insulating barrier 92, biases member 84 counterclockwise,rthat is, in the direction to position latch screw 82 above lever 76 during the resetting ope-ration; but spring 90 is made deliberately weak so as to oder negligible resistance to the `clockwise operation of member 84 in elfecting overcurrent release, and negligible resistance to the clockwise swing of member 76 during resetting.

Ambient temperature compensating bimetal 84 is united to a member 96 of electrical insulation which is also chosen as a good thermal insulator, and it is in this element 96 that pivots 86 are fixed. A projection 96a engages the active end of current responsive bimetal 32, at a point relatively remote from the end of the bimetal 32 fixed by screw 30. yIn addition, a projection 96b is formed on member 96 which rests above the right-hand extension of an armature 98 that has a pivot 100 in frame 74. Armature 98 is biased clockwise by a spring 102. Clockwise motion of armature 9S is limited by an adjustable stop member 104, and spring 102 is secured `at its righthand extremity to a portion of the adjustable stop member 104. Armature 98 is disposed above conductor 26; and this armature is movable between the side arms of a U-shaped magnetic core 106 that is set into the molded base 12 and extends about three sides of conductor 26. Current carried by conductor 26 develops a magnetic eld in core 106 that attracts armature 98 in the direction to trip member 84; and when this current is at a sufficiently high level to start armature 98 moving, the air gap between armature 98 and core 106 decreases so as to increase the armature-operating force. Spring 1012, acting along a line close to the line between the pivot 100 and the spring engagement with armature 98, develops only slightly increased tension during this action of the armature. As a result, once the armature starts to move in response to a high current level, it tends to operate with snap action. The line of action of spring 102 never crosses the point 100, so the armature is spring-restored when the overload current is interrupted.

Stop 104 is adjustably carried by a shaft 108, resting on top of frame 74. At its lower extremity member 108 is threaded into stop member 104. A compression spring 112 biases stop member 104, shaft 108, and head 110 downward.

On top of knurled head 110 there is force-fitted an adjustment knob 114, in which there is a slot 116 (formed in the shape of an arrow) for receiving the blade of a screwdriver. A projection 118 integral with knob at 114 is engageable with a fixed stop 120 projecting integrally that is formed from cover 10, `for the purpose of limiting knob 114 to approximately a 300 range of rotation. This adjusts position of stop 104, this arrangement giving the user of the circuit breaker a limited range of magnetic tripping adjustment.

With the cover open and before knob 114 is mounted in the position shown, shaft 108 can be adjusted to establish an end point of the limited range of adjustment available to the user. With the arrangement shown, a remarkably wide range of adjustment in magnetic tripping level has been realized.

The magnetic overload release is normally adjusted to a value somewhere between six and ten times the socalled normal rating of the circuit breaker. This magnetic release functions Ifor severe short-circuits for instantaneous release of the circuit breaker but does not respond to normal motor-starting currents and similar momentary overloads. It is a feature of this magnetic overload release mechanism that it can be adjusted to respond to any value o-f current over a very wide range, 250 amperes to 2,500 amperes, for example. As stop 104 is raised in position so as to increase the gap between armature 98 and core 106 (thereby to raise the cur-rent level required to overcome the spring tension) the line of action of spring 102 is also changed so `as to increase 4the component of spring tension urging armature 98 away from core 106. These factors combine in attaining an especially wide range of adjustment.

Tripping of the circuit breaker in response to its normal current rating is effected by bimetal 312 which deilects upwlard in response to heating in conductor 26, as previously mentioned. Such upward deflection drives member 84 clockwise about pivot 86, releasing the circuit breaker. The intimate engagement of bimetal 32 with conduct-or l26 makes it possible to utilize the heating that is normally 'developed -by the straight-through conductors forming the current path through the circuit breaker, and without resort to elaborate U-shaped resistors for heating the bimetal. In ian important commercial advance, a circuit breaker constructed -in the rform illustrated has a rating of 225 lamperes whereas t-he previous rating of a like circuit breaker having the same external proportions was only 100 amperes. Elimination of the previously used high-temperature resistance-element heating of the current responsive bimetal has signiicantly eliminated a built-in heat source that caused 4a high temperature rise within the enclosure. Elimination of this extra internal heat has made possible the great increase in maximum current rating of a given size of circuit breaker. Elimination of the separate heater and the Iarrangement of the currentresponsive bimetal flat against the straight-through conductor 26 has also resulted ina compact assembly.

Bimetal 32 operates lat a lower tripping temperature than 'has been customary heretofore. Accordingly this circuit breaker would have a strong tendency to respond to ambient temperature variations; and for this reason an effective ambient temperature compensation arrangement is important.

Ambient temperature compensating bimetal 84 is disposed so as to be remote `from the current-produced heating in conductor 26, compared to bimetal 32. Compensating bimetal `84 is arranged with its high-expansion side at the right in FIG. 2 so that rises in ambient temperature which would 4cause upward curving of bimetal 32 are effective to cause leftward curving of bimetal 84 so as to maintain the latching point fixed. The limited extent of deilection of bimetal 84 in response to ambient temperature changes do not have any important eifects -on the thermal current-responsive tripping level of the circuit breaker.

It has been mentioned previously that the magnetic tripping mechanism is adjustable over a wide range o-i current values for which this circuit breaker may be made. T-he identical circuit breaker mechanism can be constructed for 225 amperes and, as well, Ifor 75 amperes. It is desirable -for standardized production that the sa-me bimetal 32 shall be useful for a range of circuit breaker ratings. -In order that this may be carried out, the form of conductor 26 immediately adjacent to screw 30 may be changed so as to produce an equal temperature rise in a 75 ampere circuit breaker -as that for a 225 ampere circuit breaker of the `same construction by modifying the form of conductor y26, as by forming conductor 26 with notches and the like as represented for example in FIG. 3. Despite the fact that the conductor 26 in FIG. 3 has a sinuous current path, ie., the yconductor 26 has alternating notches 26a so that the current path is sinuous as examined closely, macroscopica-lly the current path through the circuit breaker is sti-ll substantially along a straight line when viewed, for example, as in FIG. l. The mechanical stress resistance of conductor 26 to dellecting vforces of a wire in connector 16 is effectively resisted by screws 28 regardless of the form of conductor 26 near the screw 30. Localized heating can also be produced by restricting the cross-sectional dimension `of the conductor 26 in the region of screw 30; but in the form illustrated the width of bimetal l3:2 is more eiectively heated by keeping conductor 26 wide enough to extend all the way across the bimetal that is the same where conductor 26' is used as in the case of. bar 26, used for the highest-rated circuit breaker of the class.

Operation of the circuit breaker in response to a moderate overload takes place when heating of conductor Z6 (or conductor 26') causes sumcient heating of bimetal 32 to swing pivoted ambientecompensating latch 916-84-82 out of the illustrated position to release spring-lever 76. Upon release, this spring lever drives common trip bar 62 clockwise so as to cause roller 64 to travel tow-ard the right, clear of the latched end of cradle 4d and automatic opening of the contacts follows instantly. Cradle 48 exerts relatively heavy upward pressure against roller 64 when latched. This is caused by tension in the lfour relative-lys rong springs 53, which are relied upon to drive the contacts `open and closed with snap action. The frictionless latching mechanism that includes roller 64 represents an important `feature of this apparatus, effectively restraining the cradle 43 against heavy spring pressure while atthe same time providing for virtually frictionless rele-ase by the thermal and magnetic current-responsive mecha mism. Springs 73 tor biasing the respective spring-levers 7 6 can be considerably softer than was heretofore feasible, because of the prominent reduction in the'eifort required to rotate trip bar 62 in releasing latch roller 64. The reduction'in the force exerted by springs 78 against their respective spring levers 76 results in several advantages. Prominently, the frictional force at the latch point between each spring lever 76 and the related screw 82, of the latch mmber 84 is considerably reduced las compared to a similar prior mechanism involving much heavier springs 78. Consequently, la much smaller operating Iforce exerted by bimetal 32 will reliably effect tripping of the circuit breaker in response to an overload, under conditions of minimized temperature-rise. Additionally, the magnetic tripping sensitivity is enhanced, due to the reduced strength of spring '7d and the reduced friction at latch point '76-82.

Reduction in the strength of springs 78 has the `further advantage that, when cradle '48 is reset by being swung clockwise by handle 60 the force required at handle 6i? is considerably reduced.

The straight-through current path which is here made effective for tripping the circuit breaker thermally is of advantage in respect to bra1rcl1-circuit protection where the supply line has high current capacity. Electromechanical stresses that might develop in circuit breakers having llooped resistive heaters for the bimetals are avoided here, with the straight-through form of conductors in the circuit breaker described.

The foregoing description of an illustrative circuit breaker involves an exemplary applica-tion of the invention in its various aspects; but various modifications and varied application of these features will be apparent to those skilled in the art and therefore the invention should be broadly construed in accordance with its full spirit and scope.

Having thus secured our invention, what we claim as new and desire to secure by Letters Patent is:

l. A circuit breaker including a molded case having cooperable contacts, mechanism for operating one of said contacts to open and close the circuit breaker, rst and second externally accessible terminals, and thermal overcurrent release means automatically controlling said mechanism for opening the contacts, said circuit breaker when closed having conductive portions lforming a current path extending froml said first terminal along a substantially straight line to said second terminal and said current path including an elongated conductor in the form of a xed metal bar, and said over-current release means including an elongated current responsive bimetal extending along and close to said bar and having one end thereof fixed in intimate heat transfer relation with the bar soI as tov be mechanically responsive to the thermal changes in said metal bar, said bar being substantially straight in the region of said current responsive bimetal, said overcurrent release means being disposedlaterally of saidl current responsive bimetal and being operable thereby to` effect opening of the contacts.

2. A circuit breaker including a molded case, first and second cooperable` contacts, a pair of externally accessible terminals connected to said contacts, said circuit breakerA when closed having a basically straight current path extending from said first terminal through said contacts to said second terminal and including a mov-ing contact arm, and mechanism disposed lateral of `said-current path `for operating `said moving contact arm and over-current release means for automatically controlling said mechanism for opening the contacts, said current path including an elongated conductor in the form of a metal bar extending from one. of said terminals extern-ally of the case to the interior of the case along a substantially straight line, said bar having a substantially straight and region. said metal bar being firmly secured to said molded. flat region, said metal bar being firmly secured to said.

molded case, said over-current release means including an elongated substantially straight current responsive bimetal securedat one end to said bar and extending therealong adjacent said flat portion in goo-d heat transfer relationV therewith, the opposite end' of said 'bimetal thus being mechanically responsive to the thermal changes in said metal.

bar, and arranged to effect release of the over-current release means, and an ambient temperature compensating bimetal arranged to be mechanically responsive to said,

current responsive bimetal in response to` temperature changes -within `said case, said` overcurrent release means being disposed laterally of said current responsive bimetal and being operable thereby to effect opening ofthe contacts.

3. A circuit breaker Iincluding a molded case, cooperable contacts, mechanism for operating one of said contacts to open and close the circuit breaker, first and second externally accessible terminals, and thermal overcurrent release means automatically controlling said mechanism for opening the contacts, said circuit breaker when closed having means providing a current path extending from said first terminal to said second terminal along ya substantially straight line, and said current path providing means including a metal bar secured to said molded case, an elongated current responsive bimetal ex tending along said bar in intimate heat transfer relation therewith at a point Within' the case `and mechanically responsive to the thermal changes in said metalbar, said bar and said current responsive bimetal beingpositioned at the bottom of said case, a pivoted latch member operable by said bimetal only in the tripping direction, and a member latched by said pivoted member and r.forming part of said over-current release means to release said mechanism and open the breaker on predetermined ther-` mal overloads, said latch member and said latched member being disposed in the space above said bar and said current responsive bimetal `in said case.

4. A molded case circuit breaker having cooperable contacts, mechanism for operating said contacts, a pair of externally accessible terminals, and thermal overcurrent release means, the foregoing contained in a molded case of insulation, that improvement which comprises a metal bar extending along Ia substantially straight line from one of said external terminals to the interior of said molded case towards the other of said terminals and said bar being secured to `said molded case soas to resist mechanical stress imposed by an external conductor that may be fixed tozsaid one terminal, said overcurrent release means including an elongated bimetal having one endsecured'to said`metal bar within said case, said bimetal extending closely along said bar and having one end in intimate heat transfer relation to said bar and having a portion Iarranged to deflect and thereby effect release of said overcurrent release means in response to predetermined thermal overloads.

5. A circuit breaker in accordance with claim 4 wherein a portion of said bar remote from Asaid first terminal is of reduced cross-section in close proximity to said bimetal.

6. A circuit breaker including a molded case, cooperable contacts, mechanism for operating one of said contacts to open and close the circuit breaker and including a releasable member, first and second externally accessible terminals, and thermal overcurrent release means automatically controlling said mechanism for opening the contacts, said circuit breaker when closed having a current path extending from said first terminal to said second terminal and said current path including a fixed metal bar extending from said first terminal externally of the case to the interior yof the case along a substantially str-aight line, an elongated current responsive bimetal extending along said bar in intimate heat transfer relation therewith at a point within the case and mechanically responsive to the thermal changes in sa-id metal bar, a pivoted latch member operable by said bimetal only in the tripping direction, a spring-biased member latched by said pivoted member, a trip member arranged to be operated in the release direction lby said spring-biased member, said re- Ileasable member and said trip member having opposite portions, and a latch roller yinterposed between and in rolling contact with both said opposite portions of said trip member 'and said releasable member, operation of said trip member in the tripping direction causing roll-ing trav-el of said latch roller relative to the members engaged thereby.

7. A circuit breaker including a molded case having cooperable contacts, mechanism for operating one of said contacts to open and close the circuit breaker, first and second externally accessible terminals, and thermal overcurrent release means automatically controlling said mechanism for opening the contacts, said circuit breaker when closed having conductors providing a current path extending from said first terminal to said second terminal and said current path including a fixed metal bar extending from said first terminal externally of the case to the interior of the case, an elongated current 4responsive bimetal having a portion thereof fixed in intimate heat transfer relation therewith so as to be mechanically responsive to the thermal changes in said metal bar, said operating mechanism including a releasable member, and said overcurrent release means further including latch mechanism for said releasable member comprising a trip member movable in response to overcurrent operation of said bimetal and a traveling roller interposed lbetween said release member and said trip Ymember and in rolling contact with both said release member and said trip member and providing substantially frictionless release of said releasable member in response to predetermined bimetal deflection.

8. Overload release means for a circuit breaker having a heavily spring-biased releasable member, a currentresponsive device, and release `means controlled by the current-responsive means for normally restraining the releasable member and for effecting release thereof in response to an overload, said release means including a movable member and a latch roller interposed between said movable member and said releasable member, opposite external portions of said roller having rolling-contact with both of said members, one of 'said members providing loose support for said roller and including end stops limiting the rolling travel thereof, said current-responsive means upon response to an overload being effective to cause movement of said movable member to impart rolling travel to said roller in a direction to release said releasable member, and a spring cooperating with said latch roller for biasing the roller against one of said stops following release of said releaseable member and in readiness for relatching said releasable member.

9. A circuit breaker including a molded case having cooperable contacts, mechanism for operating one of .said contacts to open and close the circuit breaker, first and second externally accessible terminals, and over-current release means automatically controlling said mechanism for opening the contacts, said circuit breaker including a fixed metal bar extending `from said first terminal externally of the case to the interior of the case along a substantially straight line, and said over-current release means including lan elongated current responsive bimetal secured to the end of said metal bar remote from said first terminal and extending closely along said bar toward said first terminal in intimate heat transfer relation with the bar, and magnetic overcurrent release means automatically controlling said -mechanism for opening the contacts comprising a magnetic core disposed about said metal bar for energization by the current therein, an armature disposed above said metal bar and above said bimetal, and a spring biasing said armature away from. said core, said release means including a pivoted latch having an elongated portion extending away from said bar and operable directly by both said bimetal `and said armature to effect automatic opening of the contacts in response to either thermal or magnetic overload.

l0. A circuit breaker in accordance with claim 9, wherein said elongated portion of said latch is an ambient temperature compensating bimetal and is disposed adjacent to a wall of said molded case.

ll. A circuit breaker including a molded case having cooperable contacts, mechanism for operating one of said lcontacts to open and close the circuit breaker, first and second externally accessible terminals, and overcurrent release means automatically controlling said mechanism for opening the contacts, said circuit breaker when closed having conductors disposed to provide a substantially straight current path extending from said first terminal to said second terminal and said current path including `a fixed metal bar extending from ysaid first ter-minal externally of the case to the interior of the case, and said overcurrent release means including an elongated cur-rent responsive bimetal extending along said bar in intimate heat transfer relation therewith so as to be mechanically responsive to the thermal changes in said metal bar, and magnetic overcurrent release means comprising a magnetic core disposed about said metal bar, and a movable armature having a spring connected thereto for biasing said armature away from said core, and means for adjusting the magnetic tripping current level of said release means comp-rising an adjustable member constituting both a -stop for said armature and a reaction means for said spring, said adjustable member being arranged for coordinately increasing said gap and the spring bias of said armature, and a common latch operable in the releasing direction by both said bimetal and said armature at respective magnetic and thermal current levels.

12. A circuit breaker including a molded case having cooperable contacts, mechanism for operating one of said contacts to open and close the circuit breaker, first and second externally accessible terminals, and thermal overcurrent release means automatically controlling said mechanism for opening the contacts, said circuit breaker when closed having conductors forming a `substantially straight current path extending from said first terminal to said second terminal and said conductors including a fixed metal bar extending from said first terminal externally of the case to the interior of the case, -said bar having -a substantially flat elongated region within said case, and said overcurrent release means including an elongated current responsive bimetal confronting 4and extending along and closely adjacent to said elongated flat region of said bar in intimate heat transfer relation therewith so as to-be mechanically responsive to the thermal changes 1n ysaid metal bar, said bar and said current responsive bimetal being positioned at the bottom of said case, `and magnetic overcurrent release means automatically controlling said mechanism for opening the contacts comprising a magnetic core disposed about said metal bar for energization by the current therein, and an armature disposed above said metal bar and spring biased away from said core, said magnetic and said thermal overcurrent release means being disposed in said casingin the spaceI above said bar.

13. A circuit breaker having cooperable contacts, and mechanism for operating one of said contacts to open and close the circuit breaker, magnetic overcurrent release means automatically controlling lsaid mechanism for opening the contacts comprising a magnetic core and a pivotally movable armature having a spring connection therewith for biasing said armature away from said core, the -action of said spring being along a line in close proximity to the line between the pivot of Said armature and said spring connection therewith whereby only slightly increased tension is developed i-n lsaid spring during armature operation in response to predetermined magnetic overloads, and commonly adjustable means cooperating with said armature and said spring connection disposed for coordinately increasing the space between said varmature, and said core and for increasing said biasing of the armature away from said core.

14. In a circuit bre-aker havingcooperable contacts, and

mechanism for operating one of said contacts to open andA close the circuit breaker, magnetic overcurrent release means automatically controlling said mechanism for opening the contacts comprising a magnetic core and a, pivotally movable armature having a spring connected thereto for biasing said armature away from said core, thev action of said spring being along a line in close proximity to the line between the pivot of said armature and the connection of said spring to said armature, and means for adjusting the magnetic tripping current level of said release means comprising an adjustable member arranged as a stop to limit the normal position of said armature.

and to stress the spring, said member being adjustable in the direction to increase the air gap between said core4 and said armature and concurrently to change the line ,of

action of the spring in the direction to increase the component of force exerted by said spring in biasing said Iarmature away from said core.

15. Magnetic overcurrent release means automatically controlling a circuit breaker for opening the contacts thereof, comprising a magnetic core and an armature having a spring connected theretofor biasing said armature away from said core, and means for adjusting the mag-v netic tripping current level of saidrelease means comprising an adjustable stop member forV lsaid armature, limiting the magnetic air gap, said spring extending tov said stop member, the latter .being movable for concomitantly increasing the air gap between said core and said armature and for increasing 4the bias of'said armature away from said core.

1'6. A circuit breaker including a molded case having coopera'ble contacts, mechanism for operating one of said contacts to open and close the circuit breaker, first and` interior of the case, a magnetic core partly surrounding said bar and a movable magnetic armature disposed opposite to said core for cooperation therewith and biased away from said core so as to be mechanically responsive to the current in said metal bar, said operating mechanism including a releasable member, kand said overcurrent release means further including latch mechanism for Asaid releasable member comprising a trip member movable in response to overcurrent operation of said `armature and a traveling roller interposed between said release member and said trip member in rollingl contact with bot-h said members and providing substantially frictionless release of Said releasable member in response to predetermined current overloads.

17. A circuit breaker including a molded case having cooperable contacts, mechanism for operating one of :said contacts to open and close the circuit breaker, first and second externally accessible terminals, and thermal overcurrent release means vautomatically controlling said mechanism' Yfor opening the conta-cts, said circuit breaker when closed having conductors providing a current path extending from-said first terminal to said second terminal and said current path includingy a xed met-al bar extending -from said first terminal externally of the case to the interior of the case, an elongated current responsive bimetal having a portion thereof fixed in intimate heat transfer relation therewith so as to be mechanically responsive to thermal changes in said bar, a magnetic .core partly surrounding said bar and a movable magnetic armature disposed oppositeto said core for cooperation therewith and biased away from said core so as to be.

mechanically responsive to the current in said metal bar, said operating mechanism including a releasable member, and said overcurrent release means further including latch mechanism for said releasable member mechanically.

coupled to said armature and to said bimetal for control and providing substantially frictionless release of Said` releasable member in response to predetermined currentoverloads.

References Cited in the tile of ythis patent UNITED STATES PATENTS 2,047,739 Lngal July 14, 1936 2,175,859 Tusing Oct. 10, 1939 2,414,554 Pierce Jan. 21, 1947 2,486,300 Lindstrom Oct. 25, 1949 l2,494,761 Jackson et al. Jan. 17, 1950 2,544,727 Rufolo Mar. 13, 1951 2,574,093 Edmunds Nov. 6, 1951 2,600,223 Dorfman June 10, 1952 2,673,908 Brumeld Mar. 30, 1954A 2,758,174 Cole Aug. 7, 1956 2,783,330 Casey Feb. 26, 1957 2,866,872 Turner Dec. 30, 1958 2,922,008 4Cellerini'et al I an. 19, 1960 

1. A CIRCUIT BREAKER INCLUDING A MOLDED CASE HAVING COOPERABLE CONTACTS, MECHANISM FOR OPERATING ONE OF SAID CONTACTS TO OPEN AND CLOSE THE CIRCUIT BREAKER, FIRST AND SECOND EXTERNALLY ACCESSIBLE TERMINALS, AND THERMAL OVERCURRENT RELEASE MEANS AUTOMATICALLY CONTROLLING SAID MECHANISM FOR OPENING THE CONTACTS, SAID CIRCUIT BREAKER WHEN CLOSED HAVING CONDUCTIVE PORTIONS FORMING A CURRENT PATH EXTENDING FROM SAID FIRST TERMINAL ALONG A SUBSTANTIALLY STRAIGHT LINE TO SAID SECOND TERMINAL AND SAID CURRENT PATH INCLUDING AN ELONGATED CONDUCTOR IN THE FORM OF A FIXED METAL BAR, AND SAID OVER-CURRENT RELEASE MEANS INCLUDING AN ELONGATED CURRENT RESPONSIVE BIMETAL EXTENDING ALONG AND CLOSE TO SAID BAR AND HAVING ONE END THEREOF FIXED IN INTIMATE HEAT TRANSFER RELATION WITH THE BAR SO AS TO BE MECHANICALLY RESPONSIVE TO THE TERMINAL CHANGES IN SAID METAL BAR, SAID BAR BEING SUBSTANTIALLY STRAIGHT IN THE REGION OF SAID CURRENT RESPONSIVE BIMETAL, SAID OVERCURRENT RELEASE MEANS BEING DISPOSED LATERALLY OF SAID CURRENT RESPONSIVE BIMETAL AND BEING OPERABLE THEREBY TO EFFECT OPENING OF THE CONTACTS. 